Yutaka Ohya

The electrical conductivity of porous and high-purity β-Ga2O3 ceramics was measured as a function of oxygen partial pressure, po2, at 700 to 900 °C. In the high po2 range, the conductivity was proportional to about −1/4th power of po2, while in the lower po2 range less than about 10−5 atm its exponent was −0.1 to −0.13. This suggests that different types of defects were formed at high and low po2. The point defect of doubly ionized interstitial gallium ion causes the exponent of −1/4, the same value of the experiment in high po2. When po2 was changed, the electrical conductivity first changed sharply, followed by a slow change, suggesting some migrations and/or formation of crystalline defects, and so on. In the Ga2O3 samples, many dislocations, with density of about 1012 cm−2, were observed. As the source of carriers, line defects, such as dislocations, should be considered as well as point defects.

The catalyst activities of various heterogeneous palladium catalysts supported by anatase-, rutile- and brookite-type titanium oxide for ligand-free Suzuki–Miyaura cross-coupling reactions of aryl chlorides were evaluated. Palladium acetate [Pd(OAc)₂], supported on anatase-type titanium oxide (TiO₂) via acetonitrile solution impregnation process without reduction [Pd/TiO₂ (anatase-type)], demonstrated the highest catalyst activity in comparison to those of other titanium oxide (rutile- or brookite-type) supported Pd(OAc)₂ without reduction and reduced Pd/TiO₂ (anatase-type) [Pd(red)/TiO₂ (anatase-type)]. Various aryl chloride and bromide derivatives were smoothly coupled with arylboronic acids including heteroarylboronic acids in the presence of 5–10 mol% Pd/TiO₂ (anatase-type) without the addition of any ligands. Although the fresh Pd/TiO₂ (anatase-type) catalyst was surprisingly comprised of ca. 1:2 mixture of palladium(II) and palladium(0) species according to X-ray photoelectron spectroscopy (XPS), in spite of no reduction process, significant further increment of palladium(0) species was observed during the Suzuki–Miyaura coupling reaction, and Pd/TiO₂ (anatase-type) was converted into a catalyst, which contained palladium(0) species as the main component [ca. 1:5 mixture of palladium(II) and palladium(0) species]. Therefore, the reduction via the electron donation process to the palladium(II) species may have occurred during the reaction on anatase-type titanium oxide.

The mesoporous titania was prepared by sol gel method using titania sol and silica sol as precursor. Mesoporous titania thin film was made by removing of silica in TiO₂-SiO₂ composite film using HF leaching. The photocatalytic performance was studied by photodegradation methylene blue in water under UV irradiation. The volume ratio of silica and the calcination temperature influenced the photoactivity. SEM images revealed as the proportion of silica increases, the proportion of the aggregated parts increase and the crystal phase was changed. The BET surface area, pore volume and pore diameter of the TiO₂-SiO₂ 7:3 at 700℃ were found to be 169.4 m²/g, 0.29 cm³/g and 3.8 nm, respectively. The best photocatalytic activity of mesoporous TiO₂ thin films is obtained when the volume ratio of oxide TiO₂-SiO₂ is 7:3 and heated at 900℃, due to the increased crystallinity of anatase and also the existance of anatase and rutile phase.

The dependence of the electrical conductivity of pure (99.999%) and tin‐doped indium oxide (In ₂ O ₃ ) ceramics on oxygen partial pressure was investigated at 800° and 850°C. The doping amount of tin was 100–1000 ppm, which is within the solubility limit at the temperatures measured. The conductivity of doped ceramics was independent of , and the carrier concentration was almost the same as the estimated value from the tin content. The conductivity of the pure In ₂ O ₃ ceramic was proportional to . By considering a singly charged defect cluster of interstitial indium and interstitial oxygen , , the conductivity dependence is deduced to be proportional to . There are large and three adjacent vacant sites, 8a and 16c, in the In ₂ O ₃ structure to enter indium and oxygen.